The invention relates to a device for aligning a wafer or substrate which contains microelectronic devices and circuits.
The term "scribing" is normally defined as cutting part way through a material such as a wafer or a substrate. By subsequently applying mechanical stresses to the material it can be broken along the scribed lines into individual pieces or dice.
The term "dicing" is normally defined as a cutting completely through a material such as a substrate thereby separating the material into individual dice in a single operation.
While the present invention will be described with respect to the scribing of substrates, it is to be understood that the principles and operations set forth are equally applicable to dicing of substrates and to other operations, such as photolithographic operations. Accordingly, the term "scribing" as used herein also includes the term "dicing."
The term "vacuum" is used herein to mean a pressure less than the atmospheric pressure at the place where the invention is being used. The pressure must be sufficiently reduced from atmospheric pressure to securely hold objects in the manner described herein.
It is common practice to form microelectronic circuits on substrates of semiconductor material (e.g., silicon) or dielectric material (e.g., sapphire or ceramic) separated by "streets" or "avenues." The wafers are then scribed along the "streets" and "avenues" and then fractured along the scribe lines thereby providing a rapid production means for separating circuits and devices. Such scribing is generally accomplished by diamond cutting tools, saws or laser beams.
Scribing equipment is generally automated so that a wafer is placed in the automated scribing equipment in proper alignment relative to the scribing apparatus to be guided automatically through the scribing apparatus. When a laser scriber is used, the wafer must be aligned in an initial position relative to the laser beam. Thereafter, automatic tape driven equipment will guide the wafer under the laser beam which will define scribe lines along the "streets" and "avenues." It is imperative, however, that the wafer be in proper alignment with respect to the laser beam in order that the scribe lines formed by the beam fall into "streets" and "avenues" of the wafer. Otherwise the scribe lines will cut through integrated circuits formed on the wafer and the circuits will be rendered useless.
The actual initial alignment of the substrate selected from a stack of substrates to be scribed is a relatively time-consuming operation. After each alignment has been completed the operator waits while the automatic scribing is carried out. After the scribing is completed the operator can remove the scribed wafer and insert the next wafer into the equipment and proceed with the aligning of the wafer. After that next wafer has been aligned the operator again initiates operation of the automatic scribing equipment and so forth.
In order to avoid the great loss of time required to align each wafer prior to scribing and to speed up production where it is necessary to scribe a stack of wafers, off station aligning devices such as the one described in U.S. Pat. No. 3,816,700 entitled APPARATUS FOR FACILITATING LASER SCRIBING, issued to Weiner et al on June 11, 1974, has heretofore been developed. In the device described by Weiner et al, an operator places a wafer to be scribed on a mounting plate which is held in a first holding chuck under a viewing microscope. The wafer is viewed by the operator through the microscope and is aligned with reference lines in the microscope by manually sliding the substrate beneath the microscope. After alignment, the substrate is vacuum sealed or otherwise held to the substrate mounting plate. Then the substrate mounting plate is transferred as a unit to a second holding chuck substantially identical to the first holding chuck thereby maintaining the orientation of the wafer. The second holding chuck is movable to a set position relative to a laser beam used to scribe the wafer.
It is always desirable to align the wafer with the side containing the microelectronic circuits facing the operator so that the "streets" and "avenues" may be easily seen and also to prevent damage to the microelectronic circuits which might occur if the wafer were aligned and manipulated with the side containing the microelectronic circuit facing down away from the operator and in contact with the work surface. In addition, if the wafer is aligned with microelectronic circuits facing up toward the operator it is not necessary to use a wafer which is transparent or translucent in order for the operator to be able to see the "streets" and "avenues." It is also desirable that the laser or other scribing or sawing take place on the reverse side of the wafer rather than on the side of the wafer containing formed microelectronic circuits because scribers and saws throw up debris which can contaminate the side of the wafer which is being scribed or sawed. Accordingly, apparatus of the type described by Weiner et al cannot easily be used for aligning wafers for scribing or sawing because the wafers are aligned with the same side facing the operator as will be scribed or sawed. On the other hand, apparatus of the type described herein is easily used for aligned wafers for sawing and scribing because the wafers are flipped over following alignment and prior to sawing or scribing. Therefore, wafers may be aligned with the microelectronic circuits facing the operator and then scribed or sawed on the reverse side of the wafer preventing contamination of the microelectronic circuits.